A communication system can be seen as a facility that enables communication sessions between two or more entities such as fixed or mobile communication devices, base stations, servers and/or other communication nodes. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. In a wireless communication system at least a part of the communication between at least two stations occurs over a wireless interface between at least two stations. Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). A wireless system can be divided into radio service areas such as cells. Hence the wireless systems are often referred to as cellular systems. A radio service area is typically provided by a base station. Radio service areas such as cells can have different shapes and sizes, and can also be divided into sectors.
A user can access the communication system by means of an appropriate communication device. Typically a communication device is used for enabling receiving and transmission of user data such as speech and content data. In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. base stations of access networks and/or other user equipments. A communication device of a user is often referred to as user equipment (UE) or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communication of data and signalling with other parties.
In addition to user data, various signalling information can be sent between the communicating devices, for example between a base station and mobile communication devices. For example, reference signals can be sent from mobile devices to base stations and vice versa.
Neighbouring radio service areas typically overlap, and thus e.g. a communication device in a cell can receive from and transmit to more than one base station. This means also that communications in a cell can interfere with communications in another cell or other radio service area.
An example of wireless communication systems is an architecture that is being standardized by the 3rd Generation Partnership Project (3GPP). This system is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. A further development of the LTE is often referred to as LTE-Advanced. The various development stages of the 3GPP LTE specifications are referred to as releases.
An interference rejection combining (IRC) receiver is considered a promising enhancement for LTE because of relatively high gain, especially for cell edge user equipments and low implementation complexity. An IRC receiver calculates and applies a set of antenna weights in the receiver to maximize the received signal to interference-plus-noise ratio (SINR) taking into account the spatial characteristics of interfering signals. An IRC receiver can be used to suppress inter-cell interference in particular. The capability of an IRC receiver is, however, dependent on the number of interfering signals and on the number of receive antennas.
On a channel such as a physical uplink shared channel (PUSCH) channel the IRC receiver is showing promising possibilities because there is typically only one interfering signal per cell due to frequency division multiplexing (FDM) separation between the user equipments. However, this may not be the case in other channels. For example, the situation on physical uplink control channel (PUCCH) is different because a signal can experience multiple interfering signals. The interferers may come from a single or a plurality of neighbouring cell. Multiple user equipments can be allocated in a PUCCH to a physical resource block (PRB), the different user equipments within one PRB being separated by different cyclic shift of cell specific zero autocorrelation (ZAC) sequences and/or different block-wise spreading codes. However, the arrangement makes the PUCCH vulnerable for interference from other user equipments.
It is possible to randomise signals from other cells by means of cell specific zero autocorrelation (ZAC) base sequence hopping and cell specific cyclic shift hopping. These may be used for PUCCH Formats 1, 2 and 3 in accordance with the 3GPP standard, the different PUCCH formats defining how control information is carried on the channel. Additionally, if communication of data is block-wise spread into a multiple of symbols, for example single carrier frequency division multiple access (SC-FDMA) symbols, the data can be cyclically or circularly shifted between the symbols according to a cell specific data hopping pattern. This can, for example, be used for PUCCH format 3 SC-FDMA symbols that are not used for reference signalling. A drawback of randomization is the possibility for high number of interfering signals. This, in turn, can mean that there is no capacity, or degrees of freedom in the spatial domain, for advanced receivers like those employing interference rejection combining (IRC) on PUCCH. Therefore PUCCH performance (e.g. coverage, capacity) can become interference limited due to a number of interfering signals from multiple user equipments allocated to the same PRB resources in adjacent cells. This can mean that there is no benefit from an advanced receiver on a PUCCH. Frequency or code domain frequency reuse can be applied for a PUCCH to address the issue, but this can increase the PUCCH overhead. For example, with reuse of ⅓, PUCCH overhead can increase by three times.
It is noted that the above discusses only examples, and the issues are not limited to any particular communication system, standard, specification, channels and so forth, but may occur in any communication system where information may be communicated by a plurality of devices on limited resources.
Embodiments of the invention aim to address one or several of the above issues.